Rheumatoid arthritis (RA) is a chronic inflammatory disease of presumed autoimmune etiology that is characterized by symmetric inflammation of the synovial joints, which may lead to damage to the cartilage and bone and a progressive loss of function. The prevalence in Western adult populations is 0.5–1 % and it is relatively similar across Europe, North America, Asia, and South Africa. However, certain native American Indians, for example Pima Indians, have a higher prevalence and, in contrast, RA appears to be rare in some rural African black populations although not in others. The annual incidence is between 0.15 and 0.88 per 1000 and women are affected two or three times as often as men. RA occurs in all age groups with a peak of disease onset between 45 and 65 years of age.